I. Field of the Invention
The present invention relates to a system for physically locating mobile objects.
II. Description of the Prior Art
There are many situations where it is highly desirable to physically locate missing objects. Such missing objects can comprise, for example, stolen articles, such as a stolen car, as well as animate objects such as pets, children and mentally incapacitated persons.
There have been a number of previously known systems for locating missing objects and many of these previously known systems rely upon the GPS satellite system currently in place in space. As is well known, the GPS satellite system generates signals such that a ground base GPS receiver is capable of receiving the GPS signal from the GPS satellite and thereafter generating a signal representative of the latitude and longitude of the GPS receiver. Such previously known systems then transmit the GPS signal to a local radio receiver either by local radio communication or by cellular phone.
One major disadvantage of these previously known systems is that, since the mobile unit attached to the object to be located only generates a local radio signal, in some cases, the actual mobile unit is outside of the receiving range of the local radio receiver. Even in the event that the mobile unit utilizes a cellular phone as the radio transmitter, there are still many areas that are still inaccessible by cellular telephones.
A still further disadvantage of these previously known systems is that such systems lack a convenient means for utilizing the latitude and longitudinal signal from the GPS receiver in order to identify the location of the missing object. As a result, specialized personnel have been previously required in order to convert the signal from the GPS receiver into meaningful information. This, in turn, increases not only the cost but the convenience of the previously known systems.
The present invention provides an object locating system which overcomes the above-mentioned disadvantages of the previously known systems.
In brief, the system of the present invention comprises a mobile unit physically connected to the object to be located. This mobile unit, in turn, includes a communication satellite transceiver capable of receiving and transmitting encoded messages. A decoder is associated with the transceiver for decoding a unique signal associated with the mobile unit, such as a telephone number, and for generating an activation signal upon receipt of the unique signal.
The mobile unit further includes a GPS receiver. Once the unique signal is received by the transceiver, the decoder activates the GPS receiver which receives the position signal from the GPS satellite representative of the latitude and longitudinal position of the mobile unit. This position signal is then coupled as an input signal to the satellite transceiver such that the satellite transceiver transmits the position signal to a base station via a communication satellite.
The base station includes both means for selectively transmitting the unique signal to the communication satellite as well as for receiving the position signal from the communication satellite. The base station then includes means for utilizing the position signal from the satellite communication transceiver for generating a display representative of the physical position of the mobile unit.
In the preferred embodiment of the invention, the base station is operated by telephone communication services and communicates with the end user via telephone lines. Thus, in order to activate the mobile unit, the end user dials a telephone number containing the unique signal which is transmitted to the mobile unit via the base station and the communication satellite. Conversely, in order to provide a display representative of the position of the mobile unit, the base station preferably generates a coded signal via telephone lines to a computer via a modem connected to the telephone line. The computer is programmed to receive the encoded position signal and then generate a display on a monitor associated with the computer representative of the physical position of the missing object.
Since the system of the present invention relies on satellite communication between the Earth and the missing object, the previously known problem of the missing object being outside the range of the local radio receiver is completely eliminated. Furthermore, since the present invention preferably communicates with the end user by a personal computer, an easy to use map display is generated on the computer monitor which eliminates the previously known need for specialized personnel to convert the position signal from the GPS receiver into meaningful information.
Direct communication between the mobile unit and the communication satellite requires a substantially unobstructed, direct line of sight signal path. In many situations, however, such a direct line unobstructed signal path is simply unavailable.
Consequently, the base station preferably includes memory storage means, such as random access memory available to a computer system, for storing the last known position signal of the mobile unit. Consequently, even in the event of a blocked signal from the mobile unit to the satellite communication system, the base station, utilizing the previously stored position of the mobile unit, will report the previously stored position of the mobile unit to the end user. While such a system is inherently inaccurate, at least the last known position of the mobile unit, as well as the time that that last known position was obtained by the base station, can be determined to provide an approximation of the position of the mobile unit.
In a modification to the preferred embodiment of the present invention, the mobile unit includes memory storage means, such as random access memory accessible by a microprocessor, for storing the last determined position of the mobile unit from the GPS receiver on a periodic basis, e.g. once every fifteen minutes. When the new position for the mobile unit is received from the GPS receiver in the mobile unit, the microprocessor calculates the change in position between the last stored position of the mobile unit and the currently determined position of the mobile unit from the GPS receiver. Only when the difference between the last stored position of the mobile unit and the current position of the mobile unit as determined from the signals received by the GPS receiver exceeds a predetermined threshold, e.g. 100 yards, does the microprocessor activate the satellite communication transmitter to transmit the current position of the mobile unit to the communication satellite. This algorithm thus achieves significant energy saving since the satellite communication transmitter in the mobile unit may be activated only sporadically, if at all, as long as movement of the mobile unit is less than the threshold amount.
In a still further modification to the present invention, the GPS receiver remains activated on a continuous basis. A microprocessor analyzes the output signal and signal strength from the GPS receiver to determine if a blocked signal condition exists. If so, activation of the satellite communication transmitter in the mobile unit is prevented thus minimizing energy consumption by the mobile unit. However, when the microprocessor determines that the blocked signal condition has been eliminated, the microprocessor immediately activates the satellite communication transmitter in the mobile unit to thereby update the position of the mobile unit at the base station. Such updating, furthermore, is preferably done on a periodic basis, e.g. once every fifteen minutes.